Lumber sorters are widely used in sawmills to sort pieces of lumber according to various criteria. For example, pieces of lumber (or “boards”) may be sorted by dimensions (e.g. width and/or length), grade or condition, tree species, and the like. A typical lumber sorter comprises a suitable number of bins for receiving sorted boards and a conveyer which carries boards that are to be sorted along a path extending across the tops of the bins. Each bin has a diverter gate which can be actuated to cause a board being carried by the conveyer to drop into the corresponding bin. A controller controls operation of the diverter gates such that each diverter gate opens at a suitable time to deliver into the corresponding bin a board that has been assigned for sorting into the bin.
There is a general desire throughout the sawmill industry to improve the efficiency of sawmills by operating at higher speeds. A disadvantage of existing lumber sorters is that the time taken for diverter gates to open and close limits the speed at which the lumber sorter can operate. Many current lumber sorters have a maximum operating speed of approximately 240 boards carried past each bin per minute. While this is reasonably fast there is a desire for lumber sorters which can operate at higher speeds still.
However, it is difficult to make sorters of existing designs operate faster. At high lug rates the diverter gates must be timed to open and close at precise times with respect to the positions of the boards so as not to lift a preceding board while it is still on the diverter gate, and not to interfere with a following board before the diverter gate is fully closed. In a modern sorter operating at rates of two hundred and forty lugs per minute or even faster, the total time available to open the diverter gate, allow a board to drop out clear of the diverter gate and close the gate again is approximately one-quarter of a second.
The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.